Field of the Invention
This invention relates to systems for increasing the efficiency of processing organic fibrous materials and especially to the utilization of waste fibrous material such as bagasse.
In the past, in order to reclaim heat that would otherwise be lost in the exhaust gases produced by the burning of bagasse in boilers, a number of approaches have been tried. One was to extract the heat from the flue gas to preheat the combustion and excess air. Another was to preheat the make-up water used in the steam plant. While some of these efforts have been successful, the system described herein offers even more efficient usage of the bagasse as a fuel.
Recently, bagasse has been known to have an increasing amount of dirt or foreign materials thus requiring a preliminary washing and wet cleaning of the cane. As a result, the cleaned bagasse has greater inherent moisture than ever before. This increased moisture content means that the bagasse, when burned, does not produce as much heat value. Furthermore, ever increasing steam loads are required as a result of anti-pollution statutes requiring the scrubbing of boiler flue gases. Currently, the deficiency in the required energy (over and above the heat value of the bagasse) is made up by using electricity from the grid. This is costly and indirectly means that more purchases of foreign oil are necessary. Alternatively, increased amounts of oil are consumed directly in the sugar mill boiler.
The approach taken by the present inventors has been different because they propose that the heat reclamation may be enhanced by upgrading the boiler fuel in both heat value and completeness of combustion. As a result of this approach, the heat value can be made to approach 50% and more complete combustion is accomplished contributing to cleaner flue gas. Using this novel system the moisture content of the bagasse applied to the boiler can be reduced from 52% to 40% or less. This, in turn, reduces evaporative losses due to the latent heat of the moisture and enables combustion at a higher temperature thereby permitting more complete combustion. The net heat value produced in a typical conventional system wherein the input bagasse has 50% moisture is about 2400 BTU/lb. The present system can improve this by 50% so as to achieve 3600 BTU/lb.
Another advantge of this novel system is that the boiler can be used closer to its maximum output rating since there is a smaller evaporative heat loss. Presently when 52% moisture bagasse is to be burned, it is customary to reduce the feed rate to the boiler because of the necessity of furnishing a large amount of excess air. If the moisture content of the bagasse is lowered to about 40%, the excess air can be cut by 35-40% and most conventional boilers may be operated close to their maximum ratings.